Boiler



FIG. 1 is a front elevation view of a boiler showing my new design;

FIG. 2 is a right side elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a top perspective view thereof;

FIG. 5 is a side perspective view thereof;

FIG. 6 is a bottom perspective view thereof; and,

FIG. 7 is a right side perspective view thereof.

In the drawings, the broken lines unclaimed subject matter only and form no part of the claimed design. 

The ornamental design for a boiler, as shown and described. 